Author(s)
Michal Botek, Pavel Stejskal, Jakub Krejčí, Aleš Jakubec, Aleš Gába
Date
2008-02-04
Source
Acta Universitatis Palackianae Olomucensis. Gymnica, Vol 38, No 2 (2008)

Exercise intensity causes changes in the activity of both branches of the autonomic nervous system (ANS) as involved in cardiovascular system regulation. Reduction in vagal activity and an increase in sympatho-adrenal activity is associated with an increase in death risk from both cardiac and arrhythmic causes during exercise. The main aim of this work was to develop a simple mathematic algorithm for determination of critical exercise intensity, at which, if exceeded, the cardiovascular system starts to be influenced dominantly by rising sympathetic activity including catecholamine and a significant withdrawal in cardiac vagal activity (vagal threshold – TVA) occurs. The testing group consisted of 10 volunteers (men). Their mean age was 27.24 ± 3.23 years and the mean value of their maximal oxygen uptake (VO2max) was 50.24 ± 4.63 ml•kg–1•min–1. ANS activity was monitored by the microprocessor diagnostics system VarCor PF 7 and assessed by a non invasive spectral analysis (SA) of heart rate variability (HRV) method. The power of the high frequency component (PHF) was calculated by integrating the area under the power spectral density curve in the frequency range from 0.15 to 0.5 Hz. Changes in autonomic cardiac regulation were assessed during walking in the steady state with exercise intensities ranging from 20 to 70% of maximal heart rate reserve (MHRR) on the treadmill. Each exercise intensity increases of about the 10% MHRR in a range from 20 to 70% MHRR led to a significant decrease in vagal activity. A designed mathematic algorithm for detecting the deflection point of the vagal activity during incremental exercise intensity revealed TVA at 43.63 ± 4.66% MHRR. We can state that the designed algorithm for detection of TVA enables an estimation of such a "safe" intensity, when the vagal activity is still preserved and sympathetic activity does not markedly rise up during exercise. The estimation of TVA could be recommended especially for the exercise prescription for patients with both reduction HRV, and at risk for sudden cardiac death.

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